1. Field of the Invention
This invention relates to an electrical switch of the maintained contact push button type, intended for emergency shut-downs and comprising a body and a command button mounted on a cylindrical body and acted upon by a return spring.
2. Discussion of the Background
A switch of the maintained contact push button type permits actuation of the electrical contacts when an operator presses the push button at the moment of an emergency shut-down. The actuating push button is mounted on a body within which a movable piston and a movable push rod are housed, the latter being used to actuate the electrical contacts. This piston and this push rod are capable of sliding and pivoting within the body, along an axis, while at the same time being immobilized relative to one another. The piston is held in the xe2x80x9conxe2x80x9d position by a catch. When an operator presses the actuating push button, the piston is moved by a cocking spring to a trip or stop position, a position in which it is held by the same catch, after having actuated the electrical contacts.
After the trip, following an emergency shut-down, the push button remains driven in, in the trip or stop position. It can be unlocked in such a way that it returns to the xe2x80x9conxe2x80x9d position, using a key inserted into a barrel or by rotation of the head.
The size of the interlock is variable mainly due to piling up of the sides and of the coefficient of friction which has a negative effect on safety.
The purpose of the invention is to provide a maintained contact push button with improved safety.
The switch according to the invention is essentially characterized by the fact that the piston is fitted with a command device capable, when the button is pushed, of actuating the first catch, called the stop catch, immobilizing the push rod in the xe2x80x9cstand-byxe2x80x9d position and then releasing the push rod which can move into the xe2x80x9ccontactxe2x80x9d position where it is immobilized by the second catch which is used to maintain contact.
According to one characteristic, the command push rod has guiding means which are guided onto helical ramps created in the body.
According to another characteristic, the body has a ramp used for the backward movement of the catch when the push rod pivots about its axis of rotation and a boss permitting the indexing of the push rod and of the piston in the contact position.